Please read 'Everything You Need to Know About Fairies' or at least skim it before coming here. Especially number 10. This explains in more detail and can help with joining.
There are six subtypes of fairies in the Hollow Tree, as well as mermaids. Fairy types are not as important as the elements they control. Fairies will usually associate themselves with their element type, not their subspecies. Some fairies are hybrids of two subtypes, and usually look like one while having the attributes of the other.
1. Sprites- Sprites are found mostly in the elements of fire or air, but not every sprite falls under those categories. They are the best flyers, and often on the smaller side. Sprites are mischievous and very agile, and while they are little, they pack a punch. They tend to be emotional and a tad immature. Sprites have stream-lined wings ready for flying long distances, and fast. In human form, they sometimes have very prominent bone structure or slightly pointy ears, but nothing out of the ordinary. They, oddly enough, are taller than most when in human form.
2. Pixies- Pixies generally control the elements of spirit or earth, although there are always exceptions. They are the sweetest fairies, and often have very powerful magic. They have colorful wings that dart around very quickly, but are not good for flying long distances. Pixies are usually hyper, cheerful, and all around trustworthy fairies. Pixies often have slightly large heads and eyes in their human form, and are on the shorter side. As fairies, pixies are normal height.
3. Dragonflies- Dragonflies are exclusively spirit or fire. They are fierce, quick-witted, and feisty. Dragonflies are quick to anger and attracted to sparkly things. They have wings like a sprite except for the fact that their wings are rather glittery, and glow in the dark. Dragonflies are average height in both human and fairy form, and commonly have a short temper. Don't piss off a dragonfly, or you'll get stung. Dragonflies make pretty, girly humans with bright eye colors who wear lots of glimmering accessories. They offer concentrated power. It's not much, but it hurts like hell.
4. Flower Fairies/Floras- Flower Fairies, nicknamed Floras, mainly control earth, although there is the occasional water Flora, called a 'Butterfly Fairy' and nicknamed Flutters. They are elegant, sweet-tempered, and calm. Floras are the only type of fairy in the Hollow Tree with butterfly wings. They often paint flowers and butterflies and work to make natural life happen. A Flora will welcome you into his or her home and cook a feast to celebrate your arrival. They are kind, welcoming, motherly/fatherly fairies who love to cook. They make a lot of the food for the fairies in the Hollow Tree, and are some of the most productive fairies out there. Humanized floras often have a natural blush and are normal height, if not a little short, in both forms.
5. Grey Fairies/Grim(m)s- Grey fairies, also called 'Grimms' or 'Grims' for their less-then-excitable attitude, generally work with Shadow or Air. Grey fairies are lackluster, pessimistic fairies who are often depressed. Grey fairies are loners, and usually manifest in low-saturation colors in fairy form. They have grey hair sometimes, no matter how old they are, and usually have silvery eyes. As humans, they have cold coloring (ice blonde, ash brown, ash blonde) instead of warm coloring (platinum blonde, auburn hair, gingers, etc.) and wide or slightly droopy eyes. They are sometimes a little taller in fairy form, normal in human, and stick-like bodies. A Grim usually has a monotone voice, droopy wings, and hardly ever laughs.
6. Fayn- Fayn, the singular form being 'Faye', are highly emotional beings that usually fall under the category of Water or Shadow. Fayn are the most colorful of fairies, and the most unpredictable. Every Faye is different. In human form, the often have either bright hair and eye colors, as well as a natural glow to them, or darkness, and a dark shadow surrounding them. Fayn are very powerful, but very vain, and are the most inclined to become evil. It is said that the king of the fairies, Oberon the 7th, is a Faye, but this may just be a rumor. Faye have bright, clearly visible wings that sometimes have a hint of color. They tend to have a lot of freckles.
Aside from these, there are also mermaids. Mermaids are NOT, I repeat, NOT fairies, but they befriend water fairies from time to time. As of now, mermaids are playable if you have at least 1 fairy character. You may only have 3 mermaid characters total. The other 7 slots must be for fairies.